Electrostatic actuator and camera module using the same

ABSTRACT

An electrostatic actuator comprises first and second stator sections having a first electrode array arranged in a first direction, and a second electrode array of electrodes extending in the first direction, respectively. A movable section having fifth and sixth electrodes arranged to face the first and second electrode arrays, respectively, is arranged between the first and second stator sections. A driving circuit alternately performs a first driving operation in which a DC voltage is applied between the adjacent electrodes of the first electrode array and a second driving operation in which a DC voltage is applied between the electrodes of the second electrode array. The voltage application is successively performed by deviating the positions of the electrodes to which the voltage is applied so as to move the movable section in the first direction while vibrating the movable section between the first and second stator sections.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-333582, filed Oct.31, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an electrostatic actuator fordriving a movable section arranged between a pair of stator sections byutilizing an electrostatic force (Coulomb force), particularly, to anelectrostatic actuator that makes it unnecessary to use an electricwiring connected to the movable section and a camera module using theparticular electrostatic actuator in the focus adjusting mechanism.

[0004] 2. Description of the Related Art

[0005] An electrostatic actuator comprising a movable section arrangedbetween a pair of stator sections, said movable section being driven byan electrostatic force (Coulomb force), is disclosed in, for example,Japanese Patent Disclosure (Kokai) No. 8-140367. The conventionalelectrostatic actuator disclosed in this prior art comprises a firststator section and a second stator section, which are arranged to faceeach other, and a movable section arranged between these first andsecond stator sections. A first electrode array consisting of aplurality of electrodes arranged at a predetermined pitch in thelongitudinal direction is mounted to the first stator section. Also, asecond electrode array consisting of a plurality of electrodes arrangedat a predetermined pitch in the longitudinal direction is mounted to thesecond stator section. It should be noted, however, that the phase ofthe electrodes of the first electrode array is deviated from the phaseof the electrodes of the second electrode array by a ½ pitch.

[0006] To be more specific, the electrodes of each of the firstelectrode array and the second electrode array are divided on theimaginary basis into four groups A, B, C and D, with every twoelectrodes in the arranging direction forming a single group, and a DCvoltage is applied between the electrodes of each of these groups andthe electrodes on the movable section.

[0007] In the conventional electrostatic actuator disclosed in thisprior art, the driving operations (1) and (2) given below arealternately repeated:

[0008] (1) A DC voltage is applied between the first electrode array andthe electrode mounted to the movable section so as to attractelectrostatically the movable section toward the first stator section;and

[0009] (2) A DC voltage is applied between the second electrode arrayand the electrode mounted to the movable section so as to attractelectrostatically the movable section toward the second stator section.

[0010] By the driving operation given above, the movable section ismacroscopically moved successively in the longitudinal direction of thestator sections by ½ pitch of the electrode array while being vibratedmicroscopically between the first stator section and the second statorsection. The moving direction of the movable section can be changed bychanging the order of applying a DV voltage to the electrodes of groupsA, B, C and D. Specifically, the movable section can be moved in a firstdirection by applying a DC voltage to the electrodes of groups A and B,the electrodes of groups B and C, the electrodes of groups C and D, andthe electrodes of group D in the order mentioned. Also, the movablesection can be moved in a second direction opposite to said firstdirection by applying a DC voltage to the electrodes of groups D and C,the electrodes of groups C and B, the electrodes of groups B and A, andthe electrodes of group A in the order mentioned.

[0011] In the conventional electrostatic actuator, utilized is theelectrostatic force generated when a DC voltage is applied between theelectrode arrays on the stator sections and the electrode on the movablesection so as to make it absolutely necessary to mount an electricalwiring to not only the electrode arrays on the stator sections but alsoto the electrode on the movable section. Since it is necessary to mountan electrical wiring to the movable section, the mass productioncapability of the electrostatic actuator is impaired. Also, since thespace for the wiring is required, the miniaturization of theelectrostatic actuator is impaired. Further, since the movable sectionis moved frequently, stress is applied to the wiring to the electrode onthe movable section, with the result that the reliability is loweredduring use of the electrostatic actuator over a long time.

[0012] It should also be noted that, in the conventional electrostaticactuator, a dielectric film is formed on the electrode as a measureagainst the insulation breakdown. What should be noted is that thedielectric polarization is generated in the dielectric film when a DCvoltage is applied between the electrode arrays on the stator sectionsand the electrode on the movable section. The dielectric polarizationproduces the force for keeping the movable section, which is attractedto one of the stator sections, attracted to the particular statorsection. The potential difference produced by the dielectricpolarization is small. However, since the distance between the movablesection and the stator section is small, it is possible for the forceproduced by the dielectric polarization to become larger than theelectrostatic force produced between the electrode on the other statorsection and the electrode on the movable section, with the result thatthe normal moving operation of the movable section tends to beobstructed.

[0013] As described above, in the conventional electrostatic actuator,in which the movable section is moved by utilizing the electrostaticforce generated when a DC voltage is applied between the electrode arrayon the stator section and the electrode on the movable section, it isabsolutely necessary to mount an electrical wiring to the electrode onthe movable section so as to give rise to the problems that the massproduction capability of the electrostatic actuator is lowered, that theelectrostatic actuator is rendered bulky because of the requirement ofthe space occupied by the electrical wiring, and that the reliability ofthe electrostatic actuator is lowered over a long time.

[0014] In addition, the conventional electrostatic actuator gives riseto the problem that the moving operation of the movable section isrendered unstable under the influence of the dielectric polarizationtaking place in the dielectric film formed on the electrode as a measureagainst the insulation breakdown.

BRIEF SUMMARY OF THE INVENTION

[0015] An object of the present invention is to provide an electrostaticactuator that makes it unnecessary to mount an electrical wiring to themovable section.

[0016] Another object of the present invention is to provide anelectrostatic actuator that permits eliminating the influence given bythe dielectric polarization of the dielectric film formed on theelectrode so as to realize a stable operation.

[0017] Further, still another object of the present invention is toprovide a camera module using the particular electrostatic actuator ofthe present invention in the focus adjusting mechanism.

[0018] According to a first aspect of the present invention, there isprovided an electrostatic actuator, comprising:

[0019] a first stator section including a first electrode arrayincluding first, second and third electrodes arranged at a predeterminedpitch in a first direction;

[0020] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a second electrode array including fourth and fifth electrodesextending in the first direction;

[0021] a movable section arranged in the space and including a firstelectrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and

[0022] a driving circuit configured to apply DC voltage signals to thefirst and second electrode arrays, alternatively, the DC voltage signalhaving a first level higher than the predetermined floating potentialand a second level lower than the predetermined floating potential,

[0023] the first DC voltage signal being applied to the adjacent firstand second electrodes of the first electrode array to attract the firstelectrode section of the movable section during a first period, thefirst and second electrodes of the first electrode array beingmaintained at the first and second levels during the first period,respectively,

[0024] the second DC voltage signal being applied to the fourth andfifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a second period, thefourth and fifth electrodes of the second electrode array beingmaintained at the first and second levels during the second period,respectively,

[0025] the third DC voltage signal being applied to the adjacent secondand third electrodes of the first electrode array to attract the firstelectrode section of the movable section during a third period, thesecond and third electrodes of the first electrode array beingmaintained at the first and second levels during the third period,respectively,

[0026] the fourth DC voltage signal being applied to the fourth andfifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a fourth period, thefourth electrode of the second electrode array being maintained at oneof the first and second levels during the fourth period, and the fifthelectrode of the second electrode array being maintained at the other offirst and second levels during the fourth period, and

[0027] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals.

[0028] According to a second aspect of the present invention, there isprovided an electrostatic actuator, comprising:

[0029] a first stator section including a first electrode arrayincluding first, second and third electrodes arranged at a predeterminedpitch in a first direction;

[0030] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a second electrode array including fourth, fifth and sixthelectrodes arranged at the predetermined pitch in the first direction;

[0031] a movable section arranged in the space and including a firstelectrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and

[0032] a driving circuit configured to apply DC voltage signals to thefirst and second electrode arrays, alternatively, the DC voltage signalhaving a first level higher than the predetermined floating potentialand a second level lower than the predetermined floating potential,

[0033] the first DC voltage signal being applied to the adjacent firstand second electrodes of the first electrode array to attract the firstelectrode section of the movable section during a first period, thefirst and second electrodes of the first electrode array beingmaintained at the first and second levels during the first period,respectively,

[0034] the second DC voltage signal being applied to the adjacent fourthand fifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a second period, thefourth and fifth electrodes of the second electrode array beingmaintained at the first and second levels during the second period,respectively,

[0035] the third DC voltage signal being applied to the adjacent secondand third electrodes of the first electrode array to attract the firstelectrode section of the movable section during a third period, thesecond and third electrodes of the first electrode array beingmaintained at the first and second levels during the third period,respectively,

[0036] the fourth DC voltage signal being applied to the adjacent fifthand sixth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a fourth period, thefifth and sixth electrodes of the second electrode array beingmaintained at the first and second levels during the fourth period,respectively, and

[0037] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals.

[0038] According to a third aspect of the present invention, there isprovided an electrostatic actuator, comprising:

[0039] a first stator section including first and second electrodearrays each including first, second and third electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection;

[0040] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a third electrode array including fourth and fifth electrodes;

[0041] a movable section arranged in the space and including a firstelectrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and

[0042] a driving circuit configured to apply DC voltage signals to thefirst and second electrode arrays and the third electrode array,alternatively, the DC voltage signal having a first level higher thanthe predetermined floating potential and a second level lower than thepredetermined floating potential,

[0043] the first DC voltage signal being applied to the first electrodesof the first and second electrode arrays to attract the first electrodesection of the movable section during a first period, the firstelectrodes of the first and second electrode arrays being maintained atthe first and second levels during the first period, respectively,

[0044] the second DC voltage signal being applied to the fourth andfifth electrodes of the third electrode array to attract the secondelectrode section of the movable section during a second period,

[0045] the third DC voltage signal being applied to the secondelectrodes of the first and second electrode arrays to attract the firstelectrode section of the movable section during a third period, thesecond electrodes of the first and second electrode arrays beingmaintained at the first and second levels during the third period,respectively, and the movable section being moved in the first directionin accordance with the application of the first, second and third DCvoltage signals.

[0046] According to a fourth aspect of the present invention, there isprovided an electrostatic actuator, comprising:

[0047] a first stator section including first and second electrodearrays each including first and second electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection;

[0048] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding third and fourth electrode arrays each including third andfourth electrodes and arranged substantially in parallel and at apredetermined pitch in the first direction, the third and fourthelectrode array being arranged at the same pitch as that of the firstand second electrode arrays in the first direction and the arrangementof the third and fourth electrode arrays being deviated by the half ofthe predetermined pitch from the arrangement of the first and secondelectrode arrays;

[0049] a movable section arranged in the space and including a firstelectrode section facing the first and second electrode arrays and asecond electrode section facing the third and fourth electrode arrays,the first and second electrode sections being maintained at apredetermined floating potential; and

[0050] a driving circuit configured to apply DC voltage signals to thefirst, second, third and fourth electrode arrays, alternatively, the DCvoltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential,

[0051] the first DC voltage being applied to the first electrodes of thefirst and second electrode arrays to attract the first electrode sectionof the movable section during a first period, the first electrodes ofthe first and second electrode arrays being maintained at the first andsecond levels during the first period, respectively,

[0052] the second DC voltage being applied to the third electrodes ofthe third and fourth electrode arrays to attract the second electrodesection of the movable section during a second period, the thirdelectrodes of the third and fourth electrode arrays being maintained atthe first and second levels during the second period, respectively,

[0053] the third DC voltage being applied to the second electrodes ofthe first and second electrode arrays to attract the first electrodesection of the movable section during a third period, the secondelectrodes of the first and second electrode arrays being maintained atthe first and second levels during the third period, respectively,

[0054] the fourth DC voltage being applied to the fourth electrodes ofthe third and fourth electrode arrays to attract the second electrodesection of the movable section during a fourth period, the fourthelectrodes of the third and fourth electrode arrays being maintained atthe first and second levels during the third period, respectively, and

[0055] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals.

[0056] According to a fifth aspect of the present invention, there isprovided an electrostatic actuator, comprising:

[0057] a first stator section including first, second and thirdelectrode arrays each including first and second electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection;

[0058] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a fourth electrode array including fourth and fifthelectrodes;

[0059] a movable section arranged in the space and including a firstelectrode section facing the first, second and third electrode arraysand a second electrode section facing the fourth and fifth electrodearrays, the first and second electrode sections being maintained at apredetermined floating potential; and

[0060] a driving circuit configured to apply DC voltage signals to thefirst, second, third and fourth electrode arrays, alternatively, the DCvoltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential,

[0061] the first DC voltage signal being applied to the first electrodesof the first, second and third electrode arrays to attract the firstelectrode section of the movable section during a first period, thefirst electrodes of the first and third electrode arrays beingmaintained at one of the first and second levels during the first periodand the first electrode of the second electrode array being maintainedat the other of the first and second levels during the first period,

[0062] the second DC voltage signal being applied to the third andfourth electrodes of the fourth electrode array to attract the secondelectrode section of the movable section during a second period,

[0063] the third DC voltage signal being applied to the secondelectrodes of the first, second and third electrode arrays to attractthe first electrode section of the movable section during a thirdperiod, the second electrodes of the first and third electrode arraysbeing maintained at one of the first and second levels during the thirdperiod, the second electrodes of the second electrode array beingmaintained at the other of the first and second levels during the thirdperiod, and the movable section being moved in the first direction inaccordance with the application of the first, second and third DCvoltage signals.

[0064] According to a sixth aspect of the present invention, there isprovided a camera module for photographing a picture image, comprising:

[0065] an electrostatic actuator, including:

[0066] a first stator section including a first electrode arrayincluding first, second and third electrodes arranged at a predeterminedpitch in a first direction;

[0067] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a second electrode array including fourth and fifth electrodesextending in the first direction;

[0068] a movable section arranged in the space and including a firstelectrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and

[0069] a driving circuit configured to apply DC voltage signals to thefirst and second electrode arrays, alternatively, the DC voltage signalhaving a first level higher than the predetermined floating potentialand a second level lower than the predetermined floating potential,

[0070] the first DC voltage signal being applied to the adjacent firstand second electrodes of the first electrode array to attract the firstelectrode section of the movable section during a first period, thefirst and second electrodes of the first electrode array beingmaintained at the first and second levels during the first period,respectively,

[0071] the second DC voltage signal being applied to the fourth andfifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a second period, thefourth and fifth electrodes of the second electrode array beingmaintained at the first and second levels during the second period,respectively,

[0072] the third DC voltage signal being applied to the adjacent secondand third electrodes of the first electrode array to attract the firstelectrode section of the movable section during a third period, thesecond and third electrodes of the first electrode array beingmaintained at the first and second levels during the third period,respectively,

[0073] the fourth DC voltage signal being applied to the fourth andfifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a fourth period, thefourth electrode of the second electrode array being maintained at oneof the first and second levels during the fourth period, and the fifthelectrode of the second electrode array being maintained at the other offirst and second levels during the fourth period, and

[0074] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals;

[0075] a lens mounted in the movable section and movable with themovable section, configured to transfer the picture image; and

[0076] an image pick-up element configured to receive the transferredpicture image to generate a image signal.

[0077] According to a seventh aspect of the present invention, there isprovided a camera module for photographing a picture image, comprising:

[0078] an electrostatic actuator, including:

[0079] a first stator section including a first electrode arrayincluding first, second and third electrodes arranged at a predeterminedpitch in a first direction;

[0080] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a second electrode array including fourth, fifth and sixthelectrodes arranged at the predetermined pitch in the first direction;

[0081] a movable section arranged in the space and including a firstelectrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and

[0082] a driving circuit configured to apply DC voltage signals to thefirst and second electrode arrays, alternatively, the DC voltage signalhaving a first level higher than the predetermined floating potentialand a second level lower than the predetermined floating potential,

[0083] the first DC voltage signal being applied to the adjacent firstand second electrodes of the first electrode array to attract the firstelectrode section of the movable section during a first period, thefirst and second electrodes of the first electrode array beingmaintained at the first and second levels during the first period,respectively,

[0084] the second DC voltage signal being applied to the adjacent fourthand fifth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a second period, thefourth and fifth electrodes of the second electrode array beingmaintained at the first and second levels during the second period,respectively,

[0085] the third DC voltage signal being applied to the adjacent secondand third electrodes of the first electrode array to attract the firstelectrode section of the movable section during a third period, thesecond and third electrodes of the first electrode array beingmaintained at the first and second levels during the third period,respectively,

[0086] the fourth DC voltage signal being applied to the adjacent fifthand sixth electrodes of the second electrode array to attract the secondelectrode section of the movable section during a fourth period, thefifth and sixth electrodes of the second electrode array beingmaintained at the first and second levels during the fourth period,respectively, and

[0087] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals;

[0088] a lens mounted in the movable section and movable with themovable section, configured to transfer the picture image; and

[0089] an image pick-up element configured to receive the transferredpicture image to generate a image signal.

[0090] According to a eighth aspect of the present invention, there isprovided a camera module for photographing a picture image, comprising:

[0091] an electrostatic actuator, including:

[0092] a first stator section including first and second electrodearrays each including first and second electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection;

[0093] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding third and fourth electrode arrays each including third andfourth electrodes and arranged substantially in parallel and at apredetermined pitch in the first direction, the third and fourthelectrode array being arranged at the same pitch as that of the firstand second electrode arrays in the first direction and the arrangementof the third and fourth electrode arrays being deviated by the half ofthe predetermined pitch from the arrangement of the first and secondelectrode arrays;

[0094] a movable section arranged in the space and including a firstelectrode section facing the first and second electrode arrays and asecond electrode section facing the third and fourth electrode arrays,the first and second electrode sections being maintained at apredetermined floating potential; and

[0095] a driving circuit configured to apply DC voltage signals to thefirst, second, third and fourth electrode arrays, alternatively, the DCvoltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential,

[0096] the first DC voltage being applied to the first electrodes of thefirst and second electrode arrays to attract the first electrode sectionof the movable section during a first period, the first electrodes ofthe first and second electrode arrays being maintained at the first andsecond levels during the first period, respectively,

[0097] the second DC voltage being applied to the third electrodes ofthe third and fourth electrode arrays to attract the second electrodesection of the movable section during a second period, the thirdelectrodes of the third and fourth electrode arrays being maintained atthe first and second levels during the second period, respectively,

[0098] the third DC voltage being applied to the second electrodes ofthe first and second electrode arrays to attract the first electrodesection of the movable section during a third period, the secondelectrodes of the first and second electrode arrays being maintained atthe first and second levels during the third period, respectively,

[0099] the fourth DC voltage being applied to the fourth electrodes ofthe third and fourth electrode arrays to attract the second electrodesection of the movable section during a fourth period, the fourthelectrodes of the third and fourth electrode arrays being maintained atthe third and fourth levels during the fourth period, respectively, and

[0100] the movable section being moved in the first direction inaccordance with the application of the first, second, third and fourthDC voltage signals;

[0101] a lens mounted in the movable section and movable with themovable section, configured to transfer the picture image; and

[0102] an image pick-up element configured to receive the transferredpicture image to generate a image signal.

[0103] According to a ninth aspect of the present invention, there isprovided a camera module for photographing a picture image, comprising:

[0104] an electrostatic actuator, including:

[0105] a first stator section including first, second and thirdelectrode arrays each including first and second electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection;

[0106] a second stator section arranged to face the first stator sectionand to define a space between the first and second stator sections, andincluding a fourth electrode array including fourth and fifthelectrodes;

[0107] a movable section arranged in the space and including a firstelectrode section facing the first, second and third electrode arraysand a second electrode section facing the fourth electrode array, thefirst and second electrode sections being maintained at a predeterminedfloating potential; and

[0108] a driving circuit configured to apply DC voltage signals to thefirst, second, third and fourth electrode arrays, alternatively, the DCvoltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential,

[0109] the first DC voltage signal being applied to the first and secondelectrodes of the first, second and third electrode arrays to attractthe first electrode section of the movable section during a firstperiod, the first and second electrodes of the first and third electrodearrays being maintained at one of the first and second levels during thefirst period and the first and second electrodes of the second electrodearray being maintained at the other of the first and second levelsduring the first period,

[0110] the second DC voltage signal being applied to the third andfourth electrodes of the fourth electrode array to attract the secondelectrode section of the movable section during a second period,

[0111] the third DC voltage signal being applied to the second and thirdelectrodes of the first, second and third electrode arrays to attractthe first electrode section of the movable section during a thirdperiod, the second and third electrodes of the first and third electrodearrays being maintained at one of the first and second levels during thethird period, the second electrodes of the second electrode array beingmaintained at the other of the first and second levels during the thirdperiod, and the movable section being moved in the first direction inaccordance with the application of the first, second and third DCvoltage signals;

[0112] a lens mounted in the movable section and movable with themovable section, configured to transfer the picture image; and

[0113] an image pick-up element configured to receive the transferredpicture image to generate a image signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0114]FIGS. 1A and 1B are cross sectional views schematically showingthe construction of the electrostatic actuator according to a firstembodiment of the present invention in a longitudinal direction of theelectrostatic actuator and in a direction perpendicular to thelongitudinal direction, respectively;

[0115]FIG. 2 schematically shows the constructions of the firstelectrode array and the second electrode array on the first statorsection and the second stator section shown in FIGS. 1A and 1B,respectively, as well as the construction of the driving circuit;

[0116]FIGS. 3A to 3F are timing charts for describing the operation ofthe electrostatic actuator shown in FIGS. 1A and 1B;

[0117]FIG. 4 schematically shows how the first step is performed foroperating the electrostatic actuator shown in FIGS. 1A and 1B;

[0118]FIG. 5 schematically shows how the second step is performed foroperating the electrostatic actuator shown in FIGS. 1A and 1B;

[0119]FIG. 6 schematically shows how the third step is performed foroperating the electrostatic actuator shown in FIGS. 1A and 1B;

[0120]FIG. 7 schematically shows how the fourth step is performed foroperating the electrostatic actuator shown in FIGS. 1A and 1B;

[0121]FIG. 8 is a cross sectional view schematically showing theconstruction of the electrostatic actuator according to a secondembodiment of the present invention in a longitudinal direction of theelectrostatic actuator;

[0122]FIG. 9 schematically shows the constructions of the firstelectrode array and the second electrode array on the first statorsection and the second stator section shown in FIG. 8, respectively, aswell as the construction of the driving circuit;

[0123]FIGS. 10A to 10H are timing charts for describing the operation ofthe electrostatic actuator shown in FIG. 8;

[0124]FIG. 11 schematically shows how the first step is performed foroperating the electrostatic actuator shown in FIG. 8;

[0125]FIG. 12 is a plan view schematically showing the construction ofthe electrode array on the first stator section in an electrostaticactuator according to a third embodiment of the present invention;

[0126]FIGS. 13A to 13J are timing charts for describing the operation ofthe electrostatic actuator shown in FIG. 12;

[0127]FIG. 14 is a plan view schematically showing the construction ofthe first electrode array on the first stator section included in anelectrostatic actuator according to a fourth embodiment of the presentinvention;

[0128]FIG. 15 is a plan view schematically showing the construction ofthe first electrode array on the first stator section included in anelectrostatic actuator according to a fifth embodiment of the presentinvention;

[0129]FIGS. 16A and 16B are a plan view schematically showing theconstruction of the first and second electrode arrays on the first andsecond stator sections included in an electrostatic actuator accordingto a sixth embodiment of the present invention;

[0130]FIGS. 17A to 17H are timing charts for describing the operation ofthe electrostatic actuator shown in FIG. 16;

[0131]FIG. 18 is a plan view schematically showing the construction ofthe first electrode array on the first stator section included in anelectrostatic actuator according to a seventh embodiment of the presentinvention;

[0132]FIG. 19 is a plan view schematically showing the construction ofthe first electrode array on the first stator section included in anelectrostatic actuator according to a eighth embodiment of the presentinvention;

[0133]FIG. 20 is a plan view schematically showing the construction ofthe first electrode array on the first stator section included in anelectrostatic actuator according to an ninth embodiment of the presentinvention; and

[0134]FIG. 21 is a plan view showing a small electronic camera moduleaccording to a tenth embodiment of the present invention, which is amodification of the electrostatic actuator of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0135] Some embodiments of the present invention will now be describedwith reference to the accompanying drawings.

[0136] (First Embodiment)

[0137]FIGS. 1A and 1B collectively show the construction of anelectrostatic actuator according to a first embodiment of the presentinvention; wherein FIG. 1A is a cross sectional view showing theelectrostatic actuator in the longitudinal direction (X-direction), andFIG. 1B is a cross section showing the electrostatic actuator in adirection (Y-direction) perpendicular to the longitudinal direction.FIG. 2 shows the planar shapes of the electrode arrays on the firststator section and the second stator section as well as the innerstructure of the driving circuit. The electrostatic actuator comprises afirst stator section 1 and a second stator section 2 arranged to faceeach other, a movable section 3 arranged in a space between the firststator section 1 and the second stator section 2 and movable in theY-direction, and a driving circuit 4.

[0138] The first stator section 1 includes an insulating substrate 11, afirst electrode array 12 formed on the substrate 11, and a dielectricfilm 13 formed to cover the first electrode array 12. As shown in FIG.2, the first electrode array 12 includes a large number of strip-likeelectrodes arranged at a predetermined pitch P in the longitudinaldirection of the substrate 11, i.e., the first direction or theX-direction. In the first electrode array 12, the electrode groups eachconsisting of the first, second, third and fourth electrodes arearranged in the electrode arranging direction (X-direction) at the sameperiod and at the same interval. For the sake of the brevity, the first,second, third and fourth electrodes are called the electrodes 12A, 12B,12C and 12D, and the capital letters A, B, C, D are put in the drawingto the wirings to these first to fourth electrodes, respectively, so asto clarify the connecting relationship.

[0139] As apparent from FIG. 1A, the first electrodes 12A are commonlyconnected by a wiring 14A so as to be connected to the driving circuit4. Similarly, the second electrodes 12B are commonly connected by thewiring 14B so as to be connected to the driving circuit 4, and the thirdelectrodes 12C are commonly connected by the wiring 14C so as to beconnected to the driving circuit 4. Further, the fourth electrodes 12Dare commonly connected by the wiring 14D so as to be connected to thedriving circuit 4. The wiring 14 is of a two layer structure having aninsulating layer interposed between the upper and lower conductivelayers. In other words, the wiring 14 is of a steric wiring structureconstructed such that one end of each of the upper and lower conductivelayers is connected to the driving circuit 4.

[0140] The second stator section 2 includes an insulating substrate 21,a second electrode array 22 formed on the insulating substrate 21, and adielectric film 23 formed to cover the upper surface of the secondelectrode array 22. As shown in FIG. 2, the second electrode array 22includes two band-like electrodes 22M and 22N formed to extend in thelongitudinal direction of the substrate 21 (first direction or theX-direction) apart from each other in the second direction (Y-direction)perpendicular to the X-direction. These electrodes 22M and 22N areconnected to the driving circuit 4.

[0141] As described above, the dielectric films 13 and 23 are formed onthe first stator section 1 and the second stator section 2,respectively. The dielectric film 13 serves to insulate the electrodesof the first electrode array 12 from each other and to insulate theelectrodes of the first electrode array 12 from a fifth electrode 33 onthe movable section 3. Similarly, the dielectric film 23 serves toinsulate the electrodes of the second electrode array 22 from each otherand to insulate each electrode of the second electrode array 22 from asixth electrode 34 on the movable section 3.

[0142] In general, where a dielectric film is formed to cover theelectrodes included in the electrostatic actuator, the moving operationof the movable section is rendered unstable under the influence of thedielectric polarization of the dielectric film. In the electrostaticactuator according to the first embodiment of the present invention,however, the voltage application pattern to the electrodes is improvedso as to overcome the problem pointed out above as described in detailherein later.

[0143] The movable section 3 is formed of a hollow parallelepipedinsulating substrate 31. The insulating substrate 31 includes a convexportion 32 on the side facing the first electrode array 12 on the firststator section 1. The fifth electrode 33 is mounted to the surface ofthe convex portion 32 facing the first electrode array 12, and the sixthelectrode 34 is mounted to the surface of the convex portion 32 facingthe second electrode array 22 on the second stator section 2. Themovable section 3 is arranged movable in the right-left direction(X-direction) in the moving space between the first stator section 1 andthe second stator section 2. As shown in FIG. 1A, the size of theelectrode surface (width L) of the convex portion 32 in the movingdirection (X-direction) of the movable section 3 is set at about 1.5 to2.0 times as much as the size (width Wa) of each of the electrodes 12A,12B, 12C and 12D in the X-direction. On the other hand, the fifthelectrode 33 and the sixth electrode 34 are not connected to the drivingcircuit 4 and are in an electrically floating state so as to formso-called “floating electrodes”.

[0144] As shown in FIG. 2, the driving circuit 4 includes two DC voltagesources 41, 42, two switching circuits 43, 44 serving to switch the DCvoltage signals generated from the DC voltage sources 41, 42 so as togenerate rectangular wave form voltage signals, and a switch controlcircuit 45 serving to control the outputs of the rectangular wave formvoltage signals generated from the switching circuits 43, 44. Theswitching circuit 43 serving to connect the first electrode array 12 tothe DC voltage source 41 via the wiring 14 includes an input terminaland an output terminal. The output generated from the output terminal iscontrolled by a control signal generated from the switch control circuit45 and supplied to the input terminal. Likewise, the switching circuit44 serving to connect the second electrode array 22 to the DC voltagesource 42 includes an input terminal and an output terminal. The outputgenerated from the output terminal is controlled by a control signalgenerated from the switch control circuit and supplied to the inputterminal. The switch control circuit 45 is constructed to control theswitching circuits 43, 44 in accordance with a drive instruction signalS1 and a direction instruction signal S2 generated from, for example, ahost computer (not shown).

[0145] The operation of the electrostatic actuator according to thefirst embodiment of the present invention will now be described withreference to the time charts shown in FIGS. 3A to 3F and to theoperating states shown in FIGS. 4 to 7. FIGS. 3A to 3F show the waveforms of the voltages applied to the electrodes 12A, 12B, 12C, 12D, 22Mand 22N, and FIGS. 4 to 7 show how the movable section 3 is moved.

[0146] In starting the operation, the drive instruction signal S1 issupplied to the switch control circuit 45 so as to render the drivingcircuit 4 active. At the same time, the direction instruction signal S2is supplied to the switch control circuit 45 so as to determine whetherthe movable section 3 is moved to the right or to the left in FIG. 1A.The following description is on the basis that the movable section 3 ismoved to the right unless otherwise pointed out specifically.

[0147] In response to the drive instruction signal S1 and the directioninstruction signal S2, a positive voltage and a negative voltage areapplied from the DC voltage source 41 to the electrode 12A and theelectrode 12B, respectively, through the switching circuit 43 for apredetermined period T1, as shown in FIGS. 3A and 3B. In this stage, theelectrode 12A, the fifth electrode 33 and the electrode 12B collectivelyform a series circuit including two capacitors, and a line E1 ofelectric force runs through the electrode 12A, the fifth electrode 33and the electrode 12B. It should be noted that the line E1 of electricforce tends to shrink as much as possible. As a result, an electrostaticattractive force is generated between the electrodes 12A, 12B and thefifth electrode 33 so as to cause the movable section 3 to be movedtoward the first stator section 1.

[0148] In the next step, positive and negative voltages are applied fromthe DC voltage source 42 to the electrode 22M and 22N, respectively,through the switching circuit 44 for a predetermined period T2, as shownin FIGS. 3E and 3F. In this stage, the circuit formed of the electrode22M, the sixth electrode 34 and the electrode 22N corresponds to anequivalent series circuit including two capacitors so as to generate aline E2 of electric force running through the electrode 22M, the sixthelectrode 34 and the electrode 22N, as shown in FIG. 5. The line E2 ofelectric force thus generate also tends to shrink and, thus, anelectrostatic attractive force is generated between the electrode 22M,22N and the sixth electrode 34. It follows that the movable section 3 ismoved toward the second stator section 2.

[0149] Further, a positive voltage and a negative voltage are applied tothe electrode 12B and the electrode 12C, respectively, during a periodT3 as shown in FIGS. 3B and 3C. As a result, line E3 of electric forceis generated to run through the electrode 12B, the fifth electrode 33and the electrode 12C, and an electrostatic attractive force isgenerated between the electrodes 12B, 12C and the fifth electrode 33. Itfollows that the movable section 3 is moved toward the first statorsection 1. It should be noted that the electrodes 12B, 12C included inthe first electrode array 12 and having voltages applied thereto aredeviated by one pitch (P) from the electrodes 12A, 12B to which thevoltages were applied previously during the period T1. It follows thatthe movable section 3 is moved to the right by one pitch P when movedtoward the first stator section 2.

[0150] In the next step, a positive voltage and a negative voltage areapplied to the electrode 22N and the electrode 22M, respectively, duringa period T4, as shown in FIGS. 3E and 3F. As a result, a line E4 ofelectric force is generated to run through the electrode 22N, the sixthelectrode 34 and the electrode 22M so as to generate an electrostaticattractive force between the electrodes 22M, 22N and the sixth electrode34. It follows that the movable section 3 is moved toward the secondstator section.

[0151] Likewise, a positive voltage and a negative voltage are appliedto the electrode 12C and the electrode 12D, respectively, during aperiod T5, as shown in FIGS. 3C and 3D and, then, a positive voltage anda negative voltage are applied to the electrode 22M and the electrode22N, respectively, during a period T6 like during the period T2, asshown in FIGS. 3E and 3F. Then, a positive voltage and a negativevoltage are applied to the electrode 12D and the electrode 12A,respectively, during a period T7, as shown in FIGS. 3D and 3A and, then,a positive voltage and a negative voltage are applied to the electrode22N and the electrode 22M, respectively, during a period T8 like duringthe period T4, as shown in FIGS. 3E and 3F. The operations describedabove are successively performed so as to finish the operation of oneperiod T consisting of the periods T1 to T8 referred to above.

[0152] By the operation described above, the movable section 3 issuccessively moved macroscopically pitch by pitch in the arrangingdirection (X-direction) of the first electrode array 12 on the firststator section 1, i.e., to the right in FIG. 1A, while being vibratedmicroscopically between the first stator section 1 and the second statorsection 2.

[0153] Where the direction instruction signal S2 instructing themovement of the movable section 3 to the right in FIG. 1A is supplied tothe switch control circuit 45, the DC voltage is applied successivelybetween the electrodes 12D and 12A, between the electrodes 22M and 22N,between the electrodes 12C and 12C, between the electrodes 22N and 22M,between the electrodes 12B and 12C, between the electrodes 22M and 22N,between the electrodes 12A and 12B, and between the electrodes 22N and22M from the period T8 toward the period T1 shown in FIGS. 3A to 3F. Asa result, the movable section 3 is successively moved macroscopically tothe left in FIG. 1A while being vibrated between the first statorsection 1 and the second stator section 2.

[0154] In the electrostatic actuator of the first embodiment describedabove, the movable section 3 is alternately attracted by utilizing theelectrostatic force generated by applying the DC voltage between theadjacent electrodes in any of the first electrode array 12 on the firststator section 1 and the second electrode array on the second statorsection 2. In other words, the movable section 3 is alternatelyattracted by the shrinking function of the lines of electric forcerunning through the fifth electrode 33 and the sixth electrode 34 on themovable section 3. Where the particular attracting function is utilizedfor attracting the movable section 3, it suffices for the fifthelectrode 33 and the sixth electrode 34 on the movable section 3 to befloating electrodes. In other words, it is unnecessary to use a wiringfor connecting these third and fourth electrodes 33 and 34 to thedriving circuit 34. It follows that the particular construction isadvantageous for the improvement in the mass production capability andthe miniaturization of the electrostatic actuator. In addition, it ispossible to solve the problem in respect of the reliability derived fromthe stress application caused by the movement of the movable section 3.

[0155] Further, if attentions are paid to a single electrode in thefirst embodiment of the present invention, the polarity of the appliedDC voltage is alternately reversed. For example, a positive voltage isapplied to the electrode 12A in the period T1 and, then, a negativevoltage is applied to the electrode 12A in the next period T3. This isalso the case with each of the electrodes 12B, 12C, 12D, 22M and 22N. Bythe particular voltage application, the charging caused by thedielectric polarization of the dielectric films 13, 23 formed as ameasure against the insulation breakdown is canceled by the applicationof the voltage of the opposite polarity. As a result, it is possible toprevent the moving operation of the movable section 3 from beingrendered unstable by the dielectric polarization.

[0156] In the first embodiment of the present invention, the sixthelectrode 34 on the movable section 3 is formed on the flat surface ofthe insulating substrate 31. As a modification of the first embodiment,it is also possible to form a convex portion on the bottom surface ofthe insulating substrate 31 in a manner to correspond to the electrodes22M and 22N constituting the second electrode array 22 on the secondstator section 2 and to form the sixth electrode 34 on the convexportion. It is also possible the entire movable section 3 to be formedof a conductive material such that the portion of the movable section 3facing the electrodes 12A, 12B, 12C and 12D of the first electrode array12 is allowed to perform the function of the fifth electrode 33, andthat the portion of the movable section 3 facing the electrodes 22M and22N of the second electrode array 22 is allowed to perform the functionof the sixth electrode 34. This is also the case with any of the otherembodiments described in the following.

[0157] (Second Embodiment)

[0158]FIG. 8 is a cross sectional view showing the electrostaticactuator according to a first embodiment of the present invention in thelongitudinal direction (X-direction), and FIG. 9 shows the planar shapesof the electrode arrays on the first stator section and the secondstator section as well as the inner structure of the driving circuit.The electrostatic actuator as shown in FIGS. 1A, 1B and 2 is so calledas one-side propagation type in which only the first stator section 1applies a propagation force to the movable section 3. In contrast, theelectrostatic actuator as shown in FIGS. 8 and 9 is so called asboth-side propagation type in which both of the first and second statorsections 1, 2 apply the propagation force to the movable section 3.

[0159] The electrostatic actuator shown in FIGS. 8 and 9 comprises afirst stator section 1 having a same configuration as that shown in FIG.2, and a second stator section 2 arranged to face the first statorsection, which includes a large number of strip-like electrodes arrangedat a predetermined pitch P in the longitudinal direction of thesubstrate 11, i.e., the first direction or the X-direction. In thesecond stator section 2, an array of electrodes 22 is arranged with asame phase as that of the first stator section 1 and has an arrangementof the electrode deviation by P/2 pitch in respect to that of the firststator section 1. In the second stator section 2, first electrodes 22Eare commonly connected by a wiring 24E so as to be connected to thedriving circuit 4. Similarly, second electrodes 22F are commonlyconnected by the wiring 24F so as to be connected to the driving circuit4, and third electrodes 22G are commonly connected by the wiring 24G soas to be connected to the driving circuit 4. Further, fourth electrodes22H are commonly connected by the wiring 24H so as to be connected tothe driving circuit 4. The wiring 24 is of a two layer structure havingan insulating layer interposed between the upper and lower conductivelayers. In other words, the wiring 24 is of a steric wiring structureconstructed such that one end of each of the upper and lower conductivelayers is connected to the driving circuit 4.

[0160] A movable section 3 is formed of a hollow parallelepipedinsulating substrate 31, as shown in FIG. 8. The insulating substrate 31includes a convex portion 32 on the side facing the first electrodearray 12 on the first stator section 1. The fifth electrode 33 ismounted to the surface of the convex portion 32 facing the firstelectrode array 12, and the sixth electrode 34 is mounted to the surfaceof the convex portion 32 facing the second electrode array 22 on thesecond stator section 2. The movable section 3 is arranged movable inthe right-left direction (X-direction) in the moving space between thefirst stator section 1 and the second stator section 2. On the otherhand, the fifth electrode 33 and the sixth electrode 34 are notconnected to the driving circuit 4 and are in an electrically floatingstate so as to form so-called “floating electrodes”.

[0161] As shown in FIG. 9, the driving circuit 4 includes two DC voltagesources 41, 42, two switching circuits 43, 44 serving to switch the DCvoltage signals generated from the DC voltage sources 41, 42 so as togenerate rectangular wave form voltage signals, and a switch controlcircuit 45 serving to control the outputs of the rectangular wave formvoltage signals generated from the switching circuits 43, 44. Theswitching circuit 43 serving to connect the first electrode array 12 tothe DC voltage source 41 via the wiring 14 includes an input terminaland an output terminal. The output generated from the output terminal iscontrolled by a control signal generated from the switch control circuit45 and supplied to the input terminal. Likewise, the switching circuit44 serving to connect the second electrode array 22 to the DC voltagesource 42 includes an input terminal and an output terminal. The outputgenerated from the output terminal is controlled by a control signalgenerated from the switch control circuit and supplied to the inputterminal. The switch control circuit 45 is constructed to control theswitching circuits 43, 44 in accordance with a drive instruction signalS1 and a direction instruction signal S2 generated from, for example, ahost computer (not shown).

[0162] The operation of the electrostatic actuator according to thesecond embodiment of the present invention will now be described withreference to the time charts shown in FIGS. 10A to 10H and to theoperating states shown in FIG. 11. FIGS. 10A to 10H show the wave formsof the voltages applied to the electrodes 12A, 12B, 12C, 12D, 22E, 22F,22G and 22H, and FIG. 11 show how the movable section 3 is moved.

[0163] In starting the operation, the drive instruction signal S1 issupplied to the switch control circuit 45 so as to render the drivingcircuit 4 active. At the same time, the direction instruction signal S2is supplied to the switch control circuit 45 so as to determine whetherthe movable section 3 is moved to the right or to the right in FIG. 8.The following description is on the basis that the movable section 3 ismoved to the right unless otherwise pointed out specifically.

[0164] In response to the drive instruction signal S1 and the directioninstruction signal S2, a positive voltage and a negative voltage areapplied from the DC voltage source 41 to the electrode 12A and theelectrode 12B, respectively, through the switching circuit 43 for apredetermined period T1, as shown in FIGS. 11A and 11B. In this stage,the electrode 12A, the electrode 33 and the electrode 12B collectivelyform a series circuit including two capacitors, and lines E1 of electricforce run through the electrode 12A, the electrode 33 and the electrode12B. It should be noted that the lines E1 of electric force tends toshrink as much as possible. As a result, an electrostatic attractiveforce is generated between the electrodes 12A, 12B and the electrode 33so as to cause the movable section 3 to be moved toward the first statorsection 1.

[0165] In the next step, positive and negative voltages are applied fromthe DC voltage source 42 to the electrode 22G and 22H, respectively,through the switching circuit 44 for a predetermined period T2, as shownin FIGS. 10G and 10H. In this stage, the circuit formed of the electrode22G, the electrode 34 and the electrode 22H corresponds to an equivalentseries circuit including two capacitors so as to generate lines E2 ofelectric force running through the electrode 22G, the electrode 34 andthe electrode 22H. The lines E2 of electric force thus generate alsotends to shrink and, thus, an electrostatic attractive force isgenerated between the electrode 22G, 22H and the electrode 34. Itfollows that the movable section 3 is moved toward the second statorsection 2. The electrodes 22G, 22H of the first electrode array 22, towhich positive and negative voltages are applied, are deviated by P/2pitch from the electrodes 12A and 12B of the first electrode array 12 towhich voltages have been applied during the period T1. Thus, the movablesection 3 is moved by P/2 pitch in the right direction at the time ofmoving the movable section 2 from the first stator section 12 toward thesecond stator section 22.

[0166] Further, a positive voltage and a negative voltage are applied tothe electrode 12B and the electrode 12C, respectively, during a periodT3 as shown in FIGS. 10B and 10C. As a result, lines E3 of electricforce are generated to run through the electrode 12B, the electrode 33and the electrode 12C, and an electrostatic attractive force isgenerated between the electrodes 12B, 12C and the electrode 33. Itfollows that the movable section 3 is moved toward the first statorsection 1. It should be noted that the electrodes 12B, 12C included inthe first electrode array 12 and having voltages applied thereto aredeviated by one pitch (P) from the electrodes 12A, 12B to which thevoltages were applied previously during the period T1. It follows thatthe movable section 3 is moved to the right when moved toward the firststator section 2.

[0167] In the next step, a positive voltage and a negative voltage areapplied to the electrode 22E and the electrode 22H, respectively, duringa period T4, as shown in FIGS. 10E and 10H. As a result, lines E4 ofelectric force are generated to run through the electrode 22E, theelectrode 34 and the electrode 22H so as to generate an electrostaticattractive force between the electrodes 22E, 22H and the electrode 34.It follows that the movable section 3 is moved toward the second statorsection 22.

[0168] Likewise, a positive voltage and a negative voltage are appliedto the electrode 12C and the electrode 12D, respectively, during aperiod T5, as shown in FIGS. 10C and 10D and, then, a positive voltageand a negative voltage are applied to the electrode 22E and theelectrode 22F, respectively, during a period T6 like during the periodT2, as shown in FIGS. 10E and 10F. Then, a positive voltage and anegative voltage are applied to the electrode 12D and the electrode 12A,respectively, during a period T7, as shown in FIGS. 10D and 10A and,then, a positive voltage and a negative voltage are applied to theelectrode 22F and the electrode 22G, respectively, during a period T8like during the period T4, as shown in FIGS. 10F and 10G. The operationsdescribed above are successively performed so as to finish the operationof one period T consisting of the periods T1 to T8 referred to above.

[0169] By the operation described above, the movable section 3 issuccessively moved macroscopically pitch by pitch in the arrangingdirection (X-direction) of the first electrode array 12 on the firststator section 1, i.e., to the right in FIG. 8, while being vibratedmicroscopically between the first stator section 1 and the second statorsection 2.

[0170] Where the direction instruction signal S2 instructing themovement of the movable section 3 to the left in FIG. 8 is supplied tothe switch control circuit 45, the DC voltage is applied successivelybetween the electrodes 12D and 12A, between the electrodes 22F and 22G,between the electrodes 12C and 12D, between the electrodes 22E and 22F,between the electrodes 12B and 12C, between the electrodes 22M and 22N,between the electrodes 12A and 12B, and between the electrodes 22H and22E from the period T8 toward the period T1 shown in FIGS. 10A to 10H.As a result, the movable section 3 is successively moved macroscopicallyto the left in FIG. 8 while being vibrated between the first statorsection 1 and the second stator section 2.

[0171] (Third Embodiment)

[0172] In the first embodiment described above, the electrodes formingthe first electrode array 12 on the first stator section 1 are alignedto form a single row in the moving direction (first direction orX-direction) of the movable section 3, and the DC voltage is appliedbetween the adjacent electrodes in the X-direction of the firstelectrode array 12. In the third embodiment of the present invention,however, a first electrode group 12-1 and a second electrode group 12-2are arranged side by side so as to form the first electrode array 12, asshown in FIG. 12. In each of the first and second electrode groups 12-1and 12-2, a plurality of electrodes are arranged in the first direction(X-direction). Also, the first and second electrode groups 12-1 and 12-2are arranged a predetermined distance apart from each other in thesecond direction (Y-direction) perpendicular to the first direction(X-direction). In the third embodiment of the present invention, a DCvoltage is applied between the electrodes included in the first andsecond electrode groups 12-1 and 12-2, i.e., between the electrodesadjacent to each other in the Y-direction. In short, the thirdembodiment clearly differs from the first embodiment in the arrangementof the electrodes on the stator section and in the manner of the voltageapplication.

[0173]FIG. 12 is a plan view showing the first electrode array 12 on thefirst stator section 1 included in the electrostatic actuator accordingto the third embodiment of the present invention. As shown in thedrawing, the first electrode array 12 includes the first electrode group12-1 consisting of electrodes 12A+, 12B+, 12C+, 12D+ and the secondelectrode group 12-2 consisting of electrodes 12A−, 12B−, 12C−, 12D−. Onthe other hand, the second electrode array 22 on the second statorsection 2 consists of two band-like electrodes 22M and 22N arranged apredetermined distance apart from each other and extending in thelongitudinal direction (X-direction) of the substrate 21 as in the firstembodiment shown in FIG. 2. Further, the fifth electrode 33 is formed onthe movable section 3 in two rows in a manner to correspond to the firstand second electrode groups 12-1 and 12-2 of the first electrode array12.

[0174] Incidentally, the symbols (+) and (−) put to the electrodes ofthe first electrode array 12 do not imply the positive (+) and negative(−) potentials used in the electric field. Specifically, these symbols(+) and (−) represent the relationship that, if the potential of theelectrode marked with the symbol (+) is positive, the potential of theelectrode marked with the symbol (−) is negative, and that, if thepotential of the electrode marked with the symbol (+) is negative, thepotential of the electrode marked with the symbol (−) is positive.

[0175] The electrodes 12A+, 12A−, the electrodes 12B+, 12B−, theelectrodes 12C+, 12C−, and the electrodes 12D+, 12D− correspond to theelectrodes 12A, 12B, 12C and 12D, respectively, of the first embodiment.The electrodes 12A+ are commonly connected to a conductive pad P2. Theelectrodes 12B+ are commonly connected to a conductive pad P1. Theelectrodes 12C+ are commonly connected to a conductive pad P3. Further,the electrodes 12D+ are commonly connected to a conductive pad P4.Likewise, the electrodes 12A−, 12B−, 12C− and 12D− are commonlyconnected to conductive pads P7, P8, P6, and P5, respectively. Theseconductive pads P1, P2, P3, P4, P5, P6, P7 and P8 are connected to thedriving circuit 4, as in FIG. 2. The driving circuit 4 comprises the DCvoltage sources 41, 42, the switching circuits 43, 44, and the switchcontrol circuit 45, as shown in FIG. 2. However, the driving circuit inthe third embodiment differs from the driving circuit 4 in the firstembodiment shown in FIG. 2 in the switching circuit 43 connected betweenthe DC voltage source 41 and the first electrode array 12. Specifically,in the third embodiment of the present invention, the switching circuit43 has 8 output terminals, not 4 output terminals.

[0176] The operation of the electrostatic actuator according to thethird embodiment of the present invention will now be described withreference to the time charts shown in FIGS. 9A to 9J. Specifically,FIGS. 9A to 9J show the wave forms of the voltages applied to theelectrode 12A+, the electrode 12A−, the electrode 12B+, the electrode12B−, the electrode 12C+, the electrode 12C−, the electrode 12D+, theelectrode 12D−, the electrode 22M and the electrode 22N, respectively.

[0177] In the first step, a positive voltage is applied to the electrode12A+ as shown in FIG. 13A, a negative voltage is applied to theelectrode 12A− as shown in FIG. 13B, a positive voltage is applied tothe electrode 12B+ as shown in FIG. 13C, and a negative voltage isapplied to the electrode 12B− as shown in FIG. 13D. In this stage, eachof the circuit formed of the electrode 12A+, the fifth electrode 33 andthe electrode 12A− and the circuit formed of the electrode 12B+, thefifth electrode 33 and the electrode 12B− forms an equivalent seriescircuit including two capacitors. As a result, generated are lines ofelectric force running through the route consisting of the electrode12A+, the fifth electrode 33, and the electrode 12A− and the routeconsisting of the electrode 12B+, the fifth electrode 33 and theelectrode 12B−. Since these lines of electric force tend to shrink asmuch as possible, an electrostatic attractive force is generated betweenthe electrodes 12A+, 12A−, 12B+, 12B− and the fifth electrode 33, withthe result that the movable section 3 is moved toward the first statorsection 1.

[0178] In the next step, a positive voltage is applied to the electrodeM22 as shown in FIG. 13I and a negative voltage is applied to theelectrode N22 as shown in FIG. 13J. In this stage, the circuit formed ofthe electrode M22, the sixth electrode 34 and the electrode N22corresponds to a series equivalent circuit including two capacitors and,thus, lines of electric force are formed to run through the electrodeM22, the sixth electrode 34 and the electrode N22. Since the lines ofelectric force thus formed tend to shrink as much as possible, anelectrostatic attractive force is generated between the electrodes M22,N22 and the sixth electrode 34, with the result that the movable section3 is moved toward the second stator section 2.

[0179] In the next step, which is not absolutely necessary, the voltagesof the polarity opposite to that of the voltages applied during theperiod T1 are applied during a period T3 such that a negative voltage isapplied to the electrode 12A+, a positive voltage is applied to theelectrode 12A−, a negative voltage is applied to the electrode 12B+, anda positive voltage is applied to the electrode 12B−. Further, thevoltages of the polarity opposite to that of the voltages applied duringthe period T2 are applied during a period T4 such that a negativevoltage is applied to the electrode 22M, a positive voltage is appliedto the electrode 22N. Since the voltages of the polarity opposite tothat of the voltages applied during the periods T1 and T2 are applied tothe electrodes 12A+, 12A−, 12B+, 12B−, 22M and 22N during the periods T3and T4, the charge generated by the dielectric polarization of thedielectric films 13, 23 formed as a measure against the insulationbreakdown is discharged, with the result that the moving operation ofthe movable section 3 is prevented from being rendered unstable by thedielectric polarization.

[0180] Then, a positive voltage is applied to the electrode 12B+ asshown in FIG. 13B, a negative voltage is applied to the electrode 12B−as shown in FIG. 13D, a positive voltage is applied to the electrode1CB+ as shown in FIG. 13E and a negative voltage is applied to theelectrode 12C− as shown in FIG. 13F. In this stage, an electrostaticattractive force is generated between the electrodes 12B+, 12B−, 12C+,12 c− and the third electrode 3e3, with the result that the movablesection 3 is moved toward the first stator section 2. It should be notedthat the electrodes 12B+, 12B−, 12C+, 12C− of the first electrode array12 to which the voltage is applied are deviated by one pitch from theelectrodes 12A+, 12A−, 12B+, 12B− to which the voltage was appliedpreviously during the period T1. It follows that the movable section 3is moved to the right by one pitch when moved toward the first statorsection 1. Then, a positive voltage is applied to the electrode M22 anda negative voltage is applied to the electrode N22 during a period T6 asshown in FIGS. 9I and 9J. As a result, an electrostatic attractive forceis generated between the electrodes 22M, 22N and the sixth electrode 34,with the result that the movable section 3 is moved toward the secondstator section 2.

[0181] Further, the voltages of the polarity opposite to that of thevoltages applied during the periods T5 and T6 are applied during aperiod T7 as during the periods T3 and T4 such that a negative voltageis applied to the electrode 12B+ as shown in FIG. 13C, a positivevoltage is applied to the electrode 12B− as shown in FIG. 13D, anegative voltage is applied to the electrode 12C+ as shown in FIG. 13E,and a positive voltage is applied to the electrode 12C− as shown in FIG.13F. Then, a negative voltage is applied to the electrode M22 and apositive voltage is applied to the electrode N22 during a period T8 asshown in FIGS. 9I and 9J so as to cancel the charge produced by thedielectric polarization of the dielectric films 13, 23. It follows thatthe moving operation of the movable section 3 is prevented from beingrendered unstable by the dielectric polarization.

[0182] Similarly, a first driving operation in which a DC voltage isapplied to two sets of the electrodes 12A+, 12B+, 12C+, 12D+ of thefirst electrode group 12-1 of the first electrode array 12 and theelectrodes 12A−, 12B−, 12C−, 12D− of the second electrode group 12-2 ofthe first electrode array 12 and a second driving operation in which aDC voltage is applied to the electrodes M22, N22 are alternatelyrepeated. In addition, the positions of the electrodes of the firstelectrode group 12-1 are successively deviated by one pitch from theelectrodes of the second electrode group 12-2 during periods T9 to T12such that the driving operation for one period T is finished by theperiods T1 to T12.

[0183] By the driving operation described above, the movable section 3is macroscopically moved to the right while being vibratedmicroscopically between the first stator section 1 and the second statorsection 2, as in the first embodiment. If the order of applying the DCvoltage to the electrodes is made opposite to that described above, themovable section 3 can be moved to the left in FIG. 12.

[0184] The third embodiment described above produces the effects similarto those produced by the first embodiment described previously. Inaddition, the third embodiment produces an additional prominent effect.Specifically, in the first embodiment of the present invention, thelines E1, E3, etc. of electric force running through the adjacentelectrodes of the first electrode array 12 via the fifth electrode 33contribute to the generation of the electrostatic attractive forcebetween the first stator section 1 and the movable section 3. It isdesirable for the size (width Wa) of each of the electrodes constitutingthe first electrode array 12 along the lines E1, E3, etc. of electricforce to be sufficiently larger than the distance between the firststator section 1 and the movable section 3. If the width Wa is small,the lines E1, E3, etc. of electric force is decreased, with the resultthat the lines of electric force running through the side surfaces ofthe adjacent electrodes of the first electrode array 12 without runningthrough the fifth electrode 33 is relatively increased. It should benoted that the lines of electric force that do not run through the fifthelectrode 33 do not contribute to the generation of the electrostaticattractive force between the first stator section 1 and the movablesection 3. It follows that it is undesirable for the lines of electricforce, which do not run through the fifth electrode 33, to be increased,because the driving force of the movable section 3 is decreased. If thearranging pitch of the electrodes of the first electrode array 12 isincreased, it is possible to increase the width Wa of the electrode soas to overcome the difficulty pointed out above. If the electrodearranging pitch is increased, however, the moving resolution of themovable section 3 is decreased. In other words, the moving amount perstep is increased.

[0185] On the other hand, in the third embodiment of the presentinvention, the lines of electric force running through the electrodes12A+, 12B+, 12C+, 12D+ of the first electrode group 12-1 of the firstelectrode array 12 and the electrodes 12A−, 12B−, 12C−, 12D− of thesecond electrode group 12-2 of the first electrode array 12 via thefifth electrode 33 contribute to the generation of the electrostaticattractive force between the first stator section 1 and the movablesection 3. In this case, it is desirable for the size (length Wb) of theelectrodes 12A+, 12B+, 12C+, 12D+, 12A−, 12B−, 12C−, 12D− along thelines of electric force to be sufficiently large, compared with thedistance between the first stator section 1 and the movable section 3.It should be note that the length Wb can be increased easily regardlessof the electrode arranging pitch P of the first electrode array 12. Itfollows that the lines of electric force running through the sidesurfaces of the adjacent electrodes of the first electrode array 12without running through the fifth electrode 33 are relatively decreasedso as to increase the driving force of the movable section 3.

[0186] (Fourth Embodiment)

[0187]FIG. 14 is a plan view showing the first electrode array 12 of thefirst stator section 1 included in the electrostatic actuator accordingto a fourth embodiment of the present invention. As shown in thedrawing, the first electrode array 12 includes a first electrode group12-1 consisting of the electrodes 12A+ and 12B+, a second electrodegroup 12-2 consisting of the electrodes 12A− and 12B−, a third electrodegroup 12-3 consisting of the electrodes 12C+ and 12D+ and a fourthelectrode group 12-4 consisting of the electrodes 12C−and 12D−. Theseelectrode groups 12-1, 12-4, 12-3 and 12-2 are arranged in the ordermentioned.

[0188] The electrodes of the electrode groups 12-1 and 12-2 have anelectrically paired relationship and are arranged to extend in theX-direction at the same pitch P and under the same phase. Likewise, theelectrodes of the electrode groups 12-3 and 12-4 have an electricallypaired relationship and are arranged to extend in the X-direction at thesame pitch P and under the same phase. However, the phase of theelectrodes of the electrode groups 12-3 and 12-4 is deviated by ½ pitch(P/2) from the phase of the electrodes of the electrode groups 12-1 and12-2.

[0189] On the other hand, the second electrode array 22 on the secondstator section 2 consists of two band-like electrodes 22M and 22N formedon the substrate 21 a predetermined distance apart from each other andextending in the longitudinal direction (X-direction) of the substrate21. Further, the fifth electrode 33 is formed in four rows on themovable section 3 in a manner to correspond to the electrode groups12-1, 12-2, 12-3, 12-4 of the first electrode array 12.

[0190] The electrode 12A+, the electrode 12B+, the electrode 12C+, theelectrode 12D+, the electrode 12A−, the electrode 12B−, the electrode12C− and the electrode 12D− correspond to the electrodes 12A, 12B, 12Cand 12D in the first embodiment. The electrode imparted with the samesymbols are commonly connected to the driving circuit through the padsP1, P2, P3, P4, P5, P6, P7 and P8.

[0191] In the first step of the fourth embodiment of the presentinvention, a positive voltage is applied to the electrode 12A+ and anegative voltage is applied to the electrode 12A− for a predeterminedperiod so as to generate lines of electric force running through theelectrode 12A+, the fifth electrode 33 and the electrode 12A−. Since thelines of electric force thus generated tend to shrink as much aspossible, an electrostatic attractive force is generated between theelectrode 12A+, 12A− and the fifth electrode 33, with the result thatthe movable section 3 is moved toward the first stator section 1. Then,a positive voltage is applied to the electrode M22 and a negativevoltage is applied to the electrode N22 so as to generate lines ofelectric force running through the electrode 22M, the sixth electrode 34and the electrode N22. Since the lines of electric force thus generatedtend to shrink as much as possible, an electrostatic force is generatedbetween the electrodes M22, N22 and the sixth electrode 34, with theresult that the movable section 3 is moved toward the second statorsection 2.

[0192] In the next step, a positive voltage is applied to the electrode12C+ and a negative voltage is applied to the electrode 12C− for apredetermined period so as to generate an electrostatic attractive forcebetween the electrodes 12C+, 12C− and the fifth electrode 33, with theresult that the movable section 3 is moved toward the first statorsection 1. Then, a negative voltage is applied to the electrode 22M anda positive voltage is applied to the electrode 22N so as to generate anelectrostatic attractive force between the electrodes 22M, 22N and thesixth electrode 34, with the result that the movable section 3 is movedtoward the second stator section 2. It should be noted that thepositions of the electrodes 12C+ and 12C− of the first electrode array12 to which the voltages are applied are deviated by ½ pitch (P/2) fromthe positions of the electrodes 12A+ and 12A− to which the voltages wereapplied previously, with the result that the movable section 3 is movedby P/2 to the right when moved toward the second stator section 2.

[0193] Likewise, a positive voltage is applied to the electrode 12B+ anda negative voltage is applied to the electrode 12B− for a predeterminedperiod so as to generate an electrostatic attractive force between theelectrodes 12B+, 12B− and the fifth electrode 33, with the result thatthe movable section 3 is moved toward the first stator section 1. Then,a positive voltage is applied to the electrode 22M and a negativevoltage is applied to the electrode 22N so as to generate anelectrostatic attractive force between the electrodes 22M, 22N and thesixth electrode 34, with the result that the movable section 3 is movedtoward the second stator section 2. Further, a positive voltage isapplied to the electrode 12D+ and a negative voltage is applied to theelectrode 12D− for a predetermined period so as to generate anelectrostatic attractive force between the electrodes 12D+, 12D− and thefifth electrode 33, with the result that the movable section 3 is movedtoward the first stator section 1. Then, a negative voltage is appliedto the electrode 22M and a positive voltage is applied to the electrode22N so as to generate an electrostatic attractive force between theelectrodes 22M, 22N and the sixth electrode 34, with the result that themovable section 3 is moved toward the second stator section 2.

[0194] By the driving operation described above, the movable section 3is macroscopically moved to the right while being vibratedmicroscopically between the first stator section 1 and the second statorsection 2, as in the first embodiment. If the order of applying the DCvoltage to the electrodes is made opposite to that described above, themovable section 3 can be moved to the left in FIG. 14.

[0195] The fourth embodiment described above produces the effectssimilar to those produced by the first embodiment described previously.Also, in the first embodiment, the movement resolution of the movablesection 3 (i.e., the moving distance per step) is equal to the electrodearranging pitch P of the first electrode array 12. In the fourthembodiment, however, the movement resolution of the movable section 3 ishalf the electrode arranging pitch P of the first electrode array 12 soas to make it possible to achieve the movement of a higher accuracy.

[0196] It should also be noted that, in the fourth embodiment of thepresent invention, the connection between the electrode and the pad canbe achieved by a planar wiring in place of a steric wiring so as toimprove the mass production capability of the electrostatic actuator.

[0197] (Fifth Embodiment)

[0198]FIG. 15 is a plan view showing the first electrode array 12 on thefirst stator section 1 included in an electrostatic actuator accordingto a fifth embodiment of the present invention. In the fifth embodimentof the present invention, two electrode groups are further added to thefirst electrode array 12 used in the fourth embodiment of the presentinvention. To be more specific, the first electrode array 12 in thefifth embodiment includes a first electrode group 12-1 consisting of theelectrodes 12A+ and 12B+, a second electrode group 12-2 consisting ofthe electrodes 12A− and 12B−, a third electrode group 12-3 consisting ofthe electrodes 12C+ and 12D+, a fourth electrode group 12-4 consistingof the electrodes 12C− and 12D−, a fifth electrode group 12-5 consistingof the electrodes 12E+ and 12F+, and a sixth electrode group 12-6consisting of the electrodes 12E−and 12F−,. These electrode groups 12-1,12-2, 12-3, 12-4, 12-5 and 12-6 are arranged in the order mentioned.

[0199] The electrodes of the electrode groups 12-1 and 12-2 have anelectrically paired relationship and are arranged to extend in theX-direction at the same pitch P and under the same phase. Likewise, theelectrodes of the electrode groups 12-3 and 12-4 have an electricallypaired relationship and are arranged to extend in the X-direction at thesame pitch P and under the same phase. Further, the electrodes of theelectrode groups 12-5 and 12-6 have an electrically paired relationshipand are arranged to extend in the X-direction at the same pitch P andunder the same phase. However, the phase of the electrodes of theelectrode groups 12-5 and 12-6 is deviated by ⅓ pitch (P/3) from thephase of the electrodes of the electrode groups 12-3 and 12-4 and, thus,is deviated by ½ pitch (2P/3) from the phase of the electrodes of theelectrode groups 12-1 and 12-2.

[0200] On the other hand, the second electrode array 22 on the secondstator section 2 consists of two band-like electrodes 22M and 22N formedon the substrate 21 a predetermined distance apart from each other andextending in the longitudinal direction (first direction) of thesubstrate 21. Further, the third electrode 34 is formed in six rows onthe movable section 3 in a manner to correspond to the electrode groups12-1, 12-2, 12-3, 12-4, 12-5 and 12-6 of the first electrode array 12.

[0201] The electrodes 12A+, 12B+, 12C+, 12D+, 12E+, 12F+, 12A−, 12B−,12C−, 12D−, 12E− and 12F− are commonly connected to the driving circuit(not shown) through pads P1 to P12, respectively.

[0202] In the first step of the fifth embodiment of the presentinvention, a positive voltage is applied to the electrode 12A+ and anegative voltage is applied to the electrode 12A− for a predeterminedperiod so as to generate lines of electric force running through theelectrode 12A+, the fifth electrode 33 and the electrode 12A− so as togenerate an electrostatic attractive force between the electrode 12A+,12A− and the fifth electrode 33, with the result that the movablesection 3 is moved toward the first stator section 1. Then, a positivevoltage is applied to the electrode M22 and a negative voltage isapplied to the electrode N22 so as to generate an electrostatic forcebetween the electrodes M22, N22 and the sixth electrode 34, with theresult that the movable section 3 is moved toward the second statorsection 2.

[0203] In the next step, a positive voltage is applied to the electrode12C+ and a negative voltage is applied to the electrode 12C− for apredetermined period so as to generate an electrostatic attractive forcebetween the electrodes 12C+, 12C− and the fifth electrode 33, with theresult that the movable section 3 is moved toward the first statorsection 1. Then, a negative voltage is applied to the electrode 22M anda positive voltage is applied to the electrode 22N so as to generate anelectrostatic attractive force between the electrodes 22M, 22N and thesixth electrode 34, with the result that the movable section 3 is movedtoward the second stator section 2.

[0204] In the next step, a positive voltage is applied to the electrode12F+ and a negative voltage is applied to the electrode 12F− for apredetermined period so as to generate an electrostatic attractive forcebetween the electrodes 12C+, 12C− and the fifth electrode 33, with theresult that the movable section 3 is moved toward the first statorsection 1. Then, a negative voltage is applied to the electrode 22M anda positive voltage is applied to the electrode 22N so as to generate anelectrostatic attractive force between the electrodes 22M, 22N and thesixth electrode 34, with the result that the movable section 3 is movedtoward the second stator section 2.

[0205] By the driving operation described above, the movable section 3is macroscopically moved to the right while being vibratedmicroscopically between the first stator section 1 and the second statorsection 2, as in the first embodiment. If the order of applying the DCvoltage to the electrodes is made opposite to that described above, themovable section 3 can be moved to the left in FIG. 15.

[0206] The fifth embodiment described above produces the effects similarto those produced by the first embodiment described previously. Also, inthe fourth first embodiment, the movement resolution of the movablesection 3 is one third of the electrode arranging pitch P of the firstelectrode array 12 so as to make it possible to achieve the movablesection movement of a higher accuracy. The technical idea of the fifthembodiment readily suggests that it is possible for the first electrodearray to be formed of a larger number of electrode groups. If the firstelectrode array is formed of an n-number of electrode groups, n being aneven number, which are arranged side by side in a manner to extend inthe longitudinal direction of the first stator section 1, the movementresolution of the movable section 3 can be further increased bydeviating the phase of each of the electrodes of the electrode groups by1/(n/2) of the electrode arranging pitch.

[0207] The fifth embodiment of the present invention is equal to thefourth embodiment in that a steric wiring is not required so as to makeit possible to improve the mass production capability of theelectrostatic actuator.

[0208] (Sixth Embodiment)

[0209]FIGS. 12A and 12B show the first electrode array 12 on the firststator section 1 and the second electrode array 22 on the second statorsection 22, respectively, according to a sixth embodiment of the presentinvention. As shown in FIG. 16A, the first electrode array 12 includes afirst electrode group 12-1 consisting of electrodes 12A+ and 12B+ eacharranged at a pitch P in a manner to extend in the X-direction and asecond electrode group 12-2 consisting of electrodes 12A− and 12B− eacharranged at a pitch P in a manner to extend in the X-direction. On theother hand, the second electrode array 22 includes a first electrodegroup 22-1 consisting of electrodes 12C+ and 12D+ each arranged at apitch P in a manner to extend in the X-direction and a second electrodegroup 22-2 consisting of electrodes 12C− and 12D− each arranged at apitch P in a manner to extend in the X-direction. It should be noted,however, that the phase of the electrodes of the second electrode array22 is deviated by ½ pitch (P/2) from the phase of the electrodes of thefirst electrode array 12.

[0210] The electrodes 12A+, the electrodes 12B+, the electrodes 12A− andthe electrodes 12B− are commonly connected to the driving circuit (notshown) through the pads P1, P2, P3 and P4, respectivelsy. Likewise, theelectrode 12C+, the electrode 12D+, the electrode 12C− and the electrode12D− belong to the groups of the electrode 12C+, the electrode 12D+, theelectrode 12C−and the electrode 12D−, respectively, and are commonlyconnected for each group to the driving circuit (not shown) through thepads P5, P6, P7 and P8.

[0211] The operation of the electrostatic actuator according to thesixth embodiment of the present invention will now be described withreference to FIGS. 17A to 17H. Specifically, FIGS. 17A to 13H show thewave forms of the voltages applied to electrode 12A+, the electrode12A−, the electrode 12B+, the electrode 12B−, the electrode 12C+, theelectrode 12C−, the electrode 12D+, the electrode 12D−, respectively.

[0212] In the first step, a positive voltage is applied to the electrode12A+ on the first stator section 1 and a negative voltage is applied tothe electrode 12A− on the first stator section 1 during a period T1 asshown in FIGS. 17A and 17B. In this stage, the circuit consisting of theelectrode 12A+, the fifth electrode 33 and the electrode 12A−equivalently corresponds to a series circuit including two capacitors soas to generate lines of electric force running through the electrode12A+, the fifth electrode 33 and the electrode 12A−. Since the lines ofelectric force thus generated tend to shrink as much as possible, anelectrostatic attractive force is generated between the electrodes 12A+,12A− and the fifth electrode 33, with the result that the movablesection 3 is moved toward the first stator section 1.

[0213] Then, a positive voltage is applied to the electrode 12C+ on thesecond stator section 2 and a negative voltage is applied to theelectrode 12C− on the second stator section 2 during a period T2 asshown in FIGS. 17E and 17F. In this stage, the circuit consisting of theelectrode 12C+, the sixth electrode 34 and the electrode 12C−equivalently corresponds to a series circuit including two capacitors soas to generate lines of electric force running through the electrode12C+, the sixth electrode 34 and the electrode 12C−. Since the lines ofelectric force thus generated tend to shrink as much as possible, anelectrostatic attractive force is generated between the electrodes 12C+,12C− and the fifth electrode 33, with the result that the movablesection 3 is moved toward the second stator section 2. It should benoted that the phase of the electrodes 12C+, 12C− is deviated by P/2from the phase of the electrodes 12A+, 12A−, with the result that themovable section 3 is moved to the right in FIG. 16 by P/2 when moved tothe second stator section 2.

[0214] In the next step, a positive voltage is applied to the electrode12B+ on the first stator section 1 and a negative voltage is applied tothe electrode 12B− on the first stator section 1 during a period T3 asshown in FIGS. 17C and 17D. In this stage, lines of electric force aregenerated in a manner to run through the electrode 12B+, the fifthelectrode 33 and the electrode 12B−. As a result, an electrostaticattractive force is generated between the electrodes 12B+, 12B− and thefifth electrode 33, with the result that the movable section 3 is movedtoward the first stator section 1. It should be noted that the phase ofthe electrodes 12B+, 12B− is deviated by P/2 from the phase of theelectrodes 12A+, 12A−, with the result that the movable section 3 ismoved to the right in FIG. 16 by P/2 when moved to the first statorsection 1.

[0215] Then, a positive voltage is applied to the electrode 12D+ on thesecond stator section 2 and a negative voltage is applied to theelectrode 12D− on the second stator section 2 during a period T4 asshown in FIGS. 17G and 17H. As a result, lines of electric force aregenerated to run through the electrode 12D+, the sixth electrode 34 andthe electrode 12D−, and an electrostatic attractive force is generatedbetween the electrodes 12D+, 12D− and the sixth electrode 34, with theresult that the movable section 3 is moved toward the second statorsection 2. It should be noted that the phase of the electrodes 12D+,12D− is deviated by P/2 from the phase of the electrodes 12C+, 12C−,with the result that the movable section 3 is moved to the right in FIG.16 by P/2 when moved to the second stator section 2.

[0216] By the driving operation described above, the movable section ismacroscopically moved to the right in FIG. 16 while being vibratedmicroscopically between the first stator section and the second statorsection. The movable section 3 can be moved to the left in FIG. 16 bymaking opposite the order of applying a DV voltage to the electrodes.

[0217] Likewise, a DC voltage is applied successively to the electrode12A+, the electrode 12A−, the electrode 12B+, the electrode 12B−, theelectrode 12C+, the electrode 12C−, the electrode 12D+ and the electrode12D− during periods T4 to T8, and the driving operation of one period Tis finished by the periods T1 to T8. It should be noted in thisconnection that the polarity of the DC voltage applied during theperiods T5 to T8 is opposite to that of the DC voltage applied duringthe periods T1 to T4, as apparent from FIGS. 17A to 17H, with the resultthat the charge produced by the dielectric polarization of thedielectric films 13, 23 is canceled as in the embodiments describedpreviously. It follows that the moving operation of the movable section3 is prevented from being rendered unstable by the dielectricpolarization.

[0218] (Seventh Embodiment)

[0219]FIG. 18 is a plan view showing the first electrode array 12 on thefirst stator section 1 according to a seventh embodiment of the presentinvention. The seventh embodiment of the present invention differs fromthe sixth embodiment in that the first electrode group 12-1 in the sixthembodiment consisting of the electrodes 12A+ and 12B+ is divided intoelectrode groups 12-1A and 12-B, and these electrode groups 12-1A and12-B are arranged on both sides of the second electrode group 12-2consisting of the electrodes 12A− and 12B−. The electrodes belonging tothe same group of the divided electrode groups 12-1A and 12-1B arecommonly connected by wirings, and these divided electrode groups 12-1Aand 12-B collectively perform the function of a single electrode group.

[0220] On the other hand, the phase of the electrodes of the secondelectrode array (not shown) on the second stator section 2 is deviatedby ½ pitch from the phase of the electrodes of the first electrode arrayas in the sixth embodiment. The driving operation of the seventhembodiment is equal to that of the sixth embodiment and, thus, thedescription is omitted in respect of the driving operation of theseventh embodiment.

[0221] The seventh embodiment produces the effects similar to thoseproduced by the first to sixth embodiments described previously and anadditional effect as described in the following. Specifically, in eachof the first to sixth embodiments, the point at which the electrostaticattractive force produced between the first stator section 1 or thesecond stator section 2 and the movable section 3 is rendered maximum ispositioned in the center in the Y-direction, with the result that it ispossible for the movable section 3 to be swung to the right or leftabout the center in the Y-direction. In the seventh embodiment, however,the point where the electrostatic attractive force is rendered maximumis positioned in two points deviant to the right and the left from thecenter in the Y-direction, with the result that the movable section 3 isunlikely to be swung. In conclusion, the seventh embodiment isadvantageous over the first to seventh embodiments in that it ispossible to stabilize the behavior and the posture of the movablesection 3.

[0222] (Eighth Embodiment)

[0223]FIG. 19 is a plan view showing the first electrode array 12 on thefirst stator section 1 according to a eighth embodiment of the presentinvention. The eighth embodiment differs from the sixth embodiment inthat the electrode 12B+ in the sixth embodiment is divided in the seconddirection (Y-direction) into three electrodes, and the dividedelectrodes 12B− are arranged between the adjacent electrodes 12A+. Thesedivided electrodes 12B− are commonly connected by a wiring andcollectively perform the function of a single electrode group.

[0224] On the other hand, the phase of the electrodes of the secondelectrode array (not shown) on the second stator section 2 is deviatedby ½ pitch from the phase of the electrodes of the first electrode arrayas in the sixth embodiment. The driving operation of the eighthembodiment is equal to that of the sixth embodiment and, thus, thedescription is omitted in respect of the driving operation of the eighthembodiment.

[0225] The eighth embodiment produces the effects similar to thoseproduced by the seventh embodiment and an additional effect as describedin the following. Specifically, it is possible to improve the wiringefficiency of the electrodes 12A+ and the electrodes 12B+ as apparentfrom FIG. 19. It follows that the eighth embodiment is advantageous inthat, if the area of the substrate 11 is the same, it is possible toincrease the effective area of the electrode, leading to an improveddriving capability of the movable section 3.

[0226] (Ninth Embodiment)

[0227]FIG. 20 is a plan view showing the construction of the secondelectrode array 22 on the second stator section 2 according to an ninthembodiment of the present invention. As shown in the drawing, the secondelectrode array 22 includes the electrodes 22M and 22N as in the firstembodiment. What should be noted is that each of these electrodes 22Mand 22N is in the shape of comb teeth, and the teeth of these electrodes22M and 22N are meshed with each other in a con-contact fashion. Thesecond electrode array 22 of the particular construction produces theeffect similar to that produced by the second electrode array 22 used inthe first embodiment.

[0228] (Tenth Embodiment)

[0229] An application of the electrostatic actuator of the presentinvention will now be described. The electrostatic actuator of thepresent invention permits producing efficient driving characteristicswith a small power consumption and, thus, is adapted for use as, forexample, the focus adjusting mechanism of a small electronic camera.

[0230]FIG. 21 shows the module portion of a small electronic camerausing the electrostatic actuator according to the ninth embodiment ofthe present invention in the focus adjusting mechanism. As shown in thedrawing, a solid state image pick-up element 101 formed of a CMOS or aCCD is arranged on a substrate 100, and an electrostatic actuator 102 ismounted to the solid state image pick-up element 101. In theelectrostatic actuator 102, a lens 5 is integrally mounted to themovable section 3 as shown in FIG. 1. Also, the driving circuit 4 of theelectrostatic actuator 102 and an IC chip 103 including, for example, aDSP (digital signal processor) chip for controlling the driving circuit4 are mounted to the substrate 100.

[0231] The electronic camera module can be formed very small as shown inFIG. 21 and is adapted for use in, for example, a portable telephone anda digital camera.

[0232] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the present invention in itsbroader aspects is not limited to the specific details andrepresentative embodiments shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. An electrostatic actuator, comprising: a firststator section including a first electrode array including first, secondand third electrodes arranged at a predetermined pitch in a firstdirection; a second stator section arranged to face the first statorsection and to define a space between the first and second statorsections, and including a second electrode array including fourth andfifth electrodes extending in the first direction; a movable sectionarranged in the space and including a first electrode section facing thefirst electrode array and a second electrode section facing the secondelectrode array, the first and second electrode sections beingmaintained at a predetermined floating potential; and a driving circuitconfigured to apply DC voltage signals to the first and second electrodearrays, alternatively, the DC voltage signal having a first level higherthan the predetermined floating potential and a second level lower thanthe predetermined floating potential, the first DC voltage signal beingapplied to the adjacent first and second electrodes of the firstelectrode array to attract the first electrode section of the movablesection during a first period, the first and second electrodes of thefirst electrode array being maintained at the first and second levelsduring the first period, respectively, the second DC voltage signalbeing applied to the fourth and fifth electrodes of the second electrodearray to attract the second electrode section of the movable sectionduring a second period, the fourth and fifth electrodes of the secondelectrode array being maintained at the first and second levels duringthe second period, respectively, the third DC voltage signal beingapplied to the adjacent second and third electrodes of the firstelectrode array to attract the first electrode section of the movablesection during a third period, the second and third electrodes of thefirst electrode array being maintained at the first and second levelsduring the third period, respectively, the fourth DC voltage signalbeing applied to the fourth and fifth electrodes of the second electrodearray to attract the second electrode section of the movable sectionduring a fourth period, the fourth electrode of the second electrodearray being maintained at one of the first and second levels during thefourth period, and the fifth electrode of the second electrode arraybeing maintained at the other of first and second levels during thefourth period, and the movable section being moved in the firstdirection in accordance with the application of the first, second, thirdand fourth DC voltage signals.
 2. The electrostatic actuator accordingto claim 1, wherein: the first electrode array further includes a sixthelectrode, the fifth DC voltage signal being applied to the adjacentthird and sixth electrodes of the first electrode array to attract thefirst electrode section of the movable section during a fifth period,the third and sixth electrodes of the first electrode array beingmaintained at the first and second levels during the fifth period,respectively.
 3. The electrostatic actuator according to claim 1,wherein: the movable section has concave and convex portions faced tothe first electrode array, the first electrode section of the movablesection formed on the convex portion.
 4. An electrostatic actuator,comprising: a first stator section including a first electrode arrayincluding first, second and third electrodes arranged at a predeterminedpitch in a first direction; a second stator section arranged to face thefirst stator section and to define a space between the first and secondstator sections, and including a second electrode array includingfourth, fifth and sixth electrodes arranged at the predetermined pitchin the first direction; a movable section arranged in the space andincluding a first electrode section facing the first electrode array anda second electrode section facing the second electrode array, the firstand second electrode sections being maintained at a predeterminedfloating potential; and a driving circuit configured to apply DC voltagesignals to the first and second electrode arrays, alternatively, the DCvoltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential, the first DC voltage signal being applied to theadjacent first and second electrodes of the first electrode array toattract the first electrode section of the movable section during afirst period, the first and second electrodes of the first electrodearray being maintained at the first and second levels during the firstperiod, respectively, the second DC voltage signal being applied to theadjacent fourth and fifth electrodes of the second electrode array toattract the second electrode section of the movable section during asecond period, the fourth and fifth electrodes of the second electrodearray being maintained at the first and second levels during the secondperiod, respectively, the third DC voltage signal being applied to theadjacent second and third electrodes of the first electrode array toattract the first electrode section of the movable section during athird period, the second and third electrodes of the first electrodearray being maintained at the first and second levels during the thirdperiod, respectively, the fourth DC voltage signal being applied to theadjacent fifth and sixth electrodes of the second electrode array toattract the second electrode section of the movable section during afourth period, the fifth and sixth electrodes of the second electrodearray being maintained at the first and second levels during the fourthperiod, respectively, and the movable section being moved in the firstdirection in accordance with the application of the first, second, thirdand fourth DC voltage signals.
 5. The electrostatic actuator accordingto claim 4, wherein: the second electrode array is arranged at the samepitch as that of the first electrode array in the first direction andthe arrangement of the second electrode array is deviated by half thepredetermined pitch from the arrangement of the first electrode array.6. The electrostatic actuator according to claim 4, wherein: the firstelectrode array further includes a seventh electrode, the secondelectrode array further includes a eighth electrode, the fifth DCvoltage signal is applied to the adjacent third and seventh electrodesof the first electrode array to attract the first electrode section ofthe movable section during a fifth period, the third and seventhelectrodes of the first electrode array being maintained at the firstand second levels during the fifth period, respectively and the sixth DCvoltage signal is applied to the fourth and eighth electrodes of thesecond electrode array to attract the second electrode section of themovable section during a sixth period, the fourth and eighth electrodesof the second electrode array being maintained at the first and secondlevels during the sixth period, respectively.
 7. The electrostaticactuator according to claim 4, wherein: the movable section has concaveand convex portions faced to the first electrode array, the firstelectrode section of the movable section formed on the convex portion.8. An electrostatic actuator, comprising: a first stator sectionincluding first and second electrode arrays each including first, secondand third electrodes and arranged substantially in parallel and at apredetermined pitch in a first direction; a second stator sectionarranged to face the first stator section and to define a space betweenthe first and second stator sections, and including a third electrodearray including fourth and fifth electrodes; a movable section arrangedin the space and including a first electrode section facing the firstelectrode array and a second electrode section facing the secondelectrode array, the first and second electrode sections beingmaintained at a predetermined floating potential; and a driving circuitconfigured to apply DC voltage signals to the first, second and thirdelectrode arrays, alternatively, the DC voltage signal having a firstlevel higher than the predetermined floating potential and a secondlevel lower than the predetermined floating potential, the first DCvoltage signal being applied to the first and second electrodes of thefirst and second electrode arrays to attract the first electrode sectionof the movable section during a first period, the first and secondelectrodes of the first and second electrode arrays being maintained atthe first and second levels during the first period, respectively, thesecond DC voltage signal being applied to the fourth and fifthelectrodes of the third electrode array to attract the second electrodesection of the movable section during a second period, the third DCvoltage signal being applied to the second and third electrodes of thefirst and second electrode arrays to attract the first electrode sectionof the movable section during a third period, the second and thirdelectrodes of the first and second electrode arrays being maintained atthe first and second levels during the third period, respectively, andthe movable section being moved in the first direction in accordancewith the application of the first, second and third DC voltage signals.9. The electrostatic actuator according to claim 8, wherein: the firstand second electrodes of the third electrode array are extended in thefirst direction.
 10. The electrostatic actuator according to claim 9,wherein: the first and second electrode arrays further includes sixthelectrodes, the fourth DC voltage signal is applied to the fourth andfifth electrodes of the third electrode array to attract the secondelectrode section of the movable section during a fourth period, and thefifth DC voltage signal is applied to the sixth electrodes of the firstand second electrode array to attract the second electrode section ofthe movable section during a fifth period.
 11. An electrostaticactuator, comprising: a first stator section including first and secondelectrode arrays each including first and second electrodes and arrangedsubstantially in parallel and at a predetermined pitch in a firstdirection; a second stator section arranged to face the first statorsection and to define a space between the first and second statorsections, and including third and fourth electrode arrays each includingthird and fourth electrodes and arranged substantially in parallel andat a predetermined pitch in the first direction, the third and fourthelectrode array being arranged at the same pitch as that of the firstand second electrode arrays in the first direction and the arrangementof the third and fourth electrode arrays being deviated by the half ofthe predetermined pitch from the arrangement of the first and secondelectrode arrays; a movable section arranged in the space and includinga first electrode section facing the first and second electrode arraysand a second electrode section facing the third and fourth electrodearrays, the first and second electrode sections being maintained at apredetermined floating potential; and a driving circuit configured toapply DC voltage signals to the first, second, third and fourthelectrode arrays, alternatively, the DC voltage signal having a firstlevel higher than the predetermined floating potential and a secondlevel lower than the predetermined floating potential, the first DCvoltage being applied to the first electrodes of the first and secondelectrode arrays to attract the first electrode section of the movablesection during a first period, the first electrodes of the first andsecond electrode arrays being maintained at the first and second levelsduring the first period, respectively, the second DC voltage beingapplied to the third electrodes of the third and fourth electrode arraysto attract the second electrode section of the movable section during asecond period, the third electrodes of the third and fourth electrodearrays being maintained at the first and second levels during the secondperiod, respectively, the third DC voltage being applied to the secondelectrodes of the first and second electrode arrays to attract the firstelectrode section of the movable section during a third period, thesecond electrodes of the first and second electrode arrays beingmaintained at the first and second levels during the third period,respectively, the fourth DC voltage being applied to the fourthelectrodes of the third and fourth electrode arrays to attract thesecond electrode section of the movable section during a fourth period,the fourth electrodes of the third and fourth electrode arrays beingmaintained at the third and fourth levels during the fourth period,respectively, and the movable section being moved in the first directionin accordance with the application of the first, second, third andfourth DC voltage signals.
 12. The electrostatic actuator according toclaim 11, wherein: the first and second electrode arrays furtherincludes a fifth electrode, the third and fourth electrode arraysfurther includes a sixth electrode, the fifth DC voltage signal isapplied to the fifth electrodes of the first and second electrode arraysto attract the first electrode section of the movable section during afifth period, the fifth electrodes of the first and second electrodearrays being maintained at the first and second levels during the fifthperiod, respectively and the sixth DC voltage signal is applied to thesixth electrodes of the third and fourth electrode arrays to attract thesecond electrode section of the movable section during a sixth period,the sixth electrodes of the third and fourth electrode arrays beingmaintained at the first and second levels during the sixth period,respectively.
 13. An electrostatic actuator, comprising: a first statorsection including first, second and third electrode arrays eachincluding first and second electrodes and arranged substantially inparallel and at a predetermined pitch in a first direction; a secondstator section arranged to face the first stator section and to define aspace between the first and second stator sections, and including afourth electrode array including fourth and fifth electrodes; a movablesection arranged in the space and including a first electrode sectionfacing the first, second and third electrode arrays and a secondelectrode section facing the fourth electrode array, the first andsecond electrode sections being maintained at a predetermined floatingpotential; and a driving circuit configured to apply DC voltage signalsto the first, second, third and fourth electrode arrays, alternatively,the DC voltage signal having a first level higher than the predeterminedfloating potential and a second level lower than the predeterminedfloating potential, the first DC voltage signal being applied to thefirst and second electrodes of the first, second and third electrodearrays to attract the first electrode section of the movable sectionduring a first period, the first and second electrodes of the first andthird electrode arrays being maintained at one of the first and secondlevels during the first period and the first and second electrodes ofthe second electrode array being maintained at the other of the firstand second levels during the first period, the second DC voltage signalbeing applied to the third and fourth electrodes of the fourth electrodearray to attract the second electrode section of the movable sectionduring a second period, the third DC voltage signal being applied to thesecond and third electrodes of the first, second and third electrodearrays to attract the first electrode section of the movable sectionduring a third period, the second and third electrodes of the first andthird electrode arrays being maintained at one of the first and secondlevels during the third period, the second electrodes of the secondelectrode array being maintained at the other of the first and secondlevels during the third period, and the movable section being moved inthe first direction in accordance with the application of the first,second and third DC voltage signals.
 14. The electrostatic actuatoraccording to claim 13, wherein: the first and second electrodes of thefourth electrode array are extended in the first direction.
 15. Theelectrostatic actuator according to claim 14, wherein: the movablesection has concave and convex portions faced to the first electrodearray, the first electrode section of the movable section formed on theconvex portion.
 16. A camera module for photographing a picture image,comprising: an electrostatic actuator, including: a first stator sectionincluding a first electrode array including first, second and thirdelectrodes arranged at a predetermined pitch in a first direction; asecond stator section arranged to face the first stator section and todefine a space between the first and second stator sections, andincluding a second electrode array including fourth and fifthelectrodes; a movable section arranged in the space and including afirst electrode section facing the first electrode array and a secondelectrode section facing the second electrode array, the first andsecond electrode sections of the movable section being maintained at apredetermined floating potential; and a driving circuit configured toapply DC voltage signals to the first and second electrode arrays,alternatively, the DC voltage signal having a first level higher thanthe predetermined floating potential and a second level lower than thepredetermined floating potential, the first DC voltage signal beingapplied to the adjacent first and second electrodes of the firstelectrode array to attract the first electrode section of the movablesection during a first period, the first and second electrodes of thefirst electrode array being maintained at the first and second levelsduring the first period, respectively, the second DC voltage signalbeing applied to the fourth and fifth electrodes of the second electrodearray to attract the second electrode section of the movable sectionduring a second period, the third DC voltage signal being applied to theadjacent second and third electrodes of the first electrode array toattract the first electrode section of the movable section during athird period, the second and third electrodes of the first electrodearray being maintained at the first and second levels during the thirdperiod, respectively, and the movable section being moved in the firstdirection in accordance with the application of the first, second andthird voltage signals. a lens mounted in the movable section and movablewith the movable section, configured to transfer the picture image; andan image pick-up element configured to receive the transferred pictureimage to generate a image signal.